I would hazard a guess that the bus was hired out for the day by a local church, youth club or school for their annual event. The background doesn’t lend itself to the usual route of the Darwen bus, but I have no idea where it is.
The Mission I attended growing up used to hire out two Blackburn buses for the annual Summer outing to Lytham which we looked forward to. There were lots of games for the young kids, football, rounders and races for the older ones. The ladies were tasked with providing the buffet. It’s unlikely that sort of simple entertainment would occur today, but it’s what h